SPM Science key terms

A testable statement predicting the relationship between variables, written before an experiment so that observations can confirm or reject it rather than being explained after the fact.

Any factor in an investigation that can change or be changed. Good experiments identify which one is manipulated, which is measured, and which are held constant.

An investigation in which only the manipulated variable is changed while all other conditions stay the same, so any effect on the measured variable can be attributed to that change.

A standard setup in which the treatment under test is left out, used for comparison so that observed changes can be attributed to the factor being investigated.

How close a measured value is to the true value. Accuracy is improved by calibrating instruments and using appropriate techniques, and is distinct from consistency between repeats.

How close repeated measurements are to one another, regardless of whether they are correct. Readings can be precise yet inaccurate if the instrument is systematically misreading.

Assigning a number and unit to a quantity using an instrument. Every reading carries uncertainty, usually taken as half the smallest scale division on an analogue device.

The internationally agreed base unit for a quantity, such as metre for length, kilogram for mass, second for time, and ampere for current, used to make results comparable worldwide.

A quantity formed by combining base quantities, such as speed (length divided by time) or density (mass divided by volume), so its unit follows from the base units.

The smallest structural and functional unit of living things. Cells contain genetic material and carry out the chemical reactions that sustain life.

A thin, partially permeable layer surrounding the cell that controls which substances enter and leave, keeping the internal environment different from the outside.

The organelle that contains chromosomes made of DNA. It directs cell activities and is the site where genetic instructions are stored and copied.

The net movement of particles from a region of higher concentration to lower concentration, driven by random motion, until the concentrations become even.

The movement of water molecules across a partially permeable membrane from a dilute solution to a more concentrated one, important for water uptake in plants and cells.

The process in green plants that uses light energy to convert carbon dioxide and water into glucose and oxygen, with chlorophyll as the light-absorbing pigment.

The green pigment inside chloroplasts that absorbs light energy for photosynthesis. It absorbs mainly red and blue light and reflects green wavelengths.

The controlled release of energy from glucose in all living cells. Aerobic respiration uses oxygen and releases more energy than anaerobic respiration.

A protein that speeds up a specific reaction in living things. Enzymes are sensitive to temperature and pH, and are denatured at high temperatures.

The breakdown of large, insoluble food molecules into small, soluble ones that can be absorbed into the blood, carried out mechanically and by enzymes.

The smallest particle of an element that retains the properties of that element. It consists of a nucleus of protons and neutrons surrounded by electrons.

A pure substance made of only one kind of atom, which cannot be split into simpler substances by chemical means and is listed in the periodic table.

A substance formed when two or more different elements are chemically joined in fixed proportions, giving properties different from those of the constituent elements.

Two or more substances combined without chemical bonding, in any proportion. Components of a mixture keep their own properties and can be separated by physical methods.

A separation method that traps insoluble solid particles on filter paper while the liquid or solution passes through, used to separate a solid from a suspension.

A separation method that boils a liquid mixture and condenses the vapour, used to separate a solvent from dissolved solids or to separate liquids with different boiling points.

A substance that releases hydrogen ions in water, turns blue litmus red, and reacts with bases to form a salt and water in a neutralisation reaction.

A substance that reacts with an acid to form a salt and water. Soluble bases are alkalis and turn red litmus blue.

A scale from 0 to 14 measuring how acidic or alkaline a solution is. Values below 7 are acidic, 7 is neutral, and values above 7 are alkaline.

A push or a pull that can change an object's shape, speed, or direction. Force is measured in newtons using a spring balance or force sensor.

The SI unit of force. One newton is the force needed to accelerate a mass of one kilogram at one metre per second squared.

A force that opposes motion between surfaces in contact. It produces heat and can be reduced with lubricants or smoothed surfaces, or increased when grip is needed.

The attractive force between masses. On Earth it gives falling objects an acceleration of about 9.8 metres per second squared and gives objects their weight.

The gravitational force acting on a mass, calculated as mass multiplied by gravitational field strength and measured in newtons, unlike mass which is in kilograms.

The amount of matter in an object, measured in kilograms and unchanged by location, unlike weight which depends on the local gravitational field.

The distance travelled per unit time, calculated as distance divided by time. Average speed smooths out changes over a journey.

The rate of change of velocity, calculated as change in velocity divided by time taken and measured in metres per second squared.

The capacity to do work, measured in joules. Energy is conserved overall but can be transferred between stores and dissipated as heat by friction.

The rate at which energy is transferred or work is done, calculated as energy divided by time and measured in watts.